Generally, when a tire wears off, its tire performance changes greatly, for example, drain-performance in a damp road declines in accordance with its degree of wear. Accordingly, to enhance safety of a vehicle, it is important to detect condition of the tire contacting with a road surface, particularly its degree of wear. Progress of wear of the tire causes burst of the tire.
As a method of estimating tire wear, there is proposed that a method for estimating tire wear by burying a sensor 53 including a resistance means 51 that a plurality of conductive rubber resistance 51a are connected to resistance 51b in parallel and direct power supply directly connected to the resistance means 51, and a tire mounting unit 50 including a transmitter 55 transmitting detection signal of the sensor 53 through an antenna 54 in a block 61 of a tire tread 60, detecting resistance value of the resistance means 51 that changes in accordance with wear of the block 61 and estimating wear amount of the tire tread 60 (make reference with, for example, patent document 1) as shown in the FIGS. 6(a) and (b).    Patent document 1: Patent application publication JP2005-28950